HMat: Write distance matrix and kernel matrix in same test; Use distance matrix for clustering (in testCCL).

HMat: Allow truncation in SVDBlocks (default accuracy is 1e-14); Add timings; Fixed minor merge conflicts.

HMat: Provided SVDBlock class to represent blocks by low rank approx based on SVD; Fixed gemm (not tested).

HMat: Provided some spatial grids along with programs to generate associated kernel matrices; fixed CMakeLists.